Phase alignment circuit and method of receive end, and receive end

ABSTRACT

This application discloses a phase alignment circuit and a method of a receive end, and a receive end. The receive end is located on an electric vehicle. The phase alignment circuit includes a phase measurement circuit and a controller. The controller is configured to: use, as an actual phase shift angle, a result obtained by subtracting a phase difference from a preset phase shift angle, and control a phase of a bridge arm voltage of a rectifier to lag behind the phase of the input current fundamental component by the actual phase shift angle. The controller outputs a drive signal for a controllable switching transistor of the rectifier by using the actual phase shift angle. Because a lagging phase caused due to filtering is compensated for, precision of synchronization between the bridge arm voltage and the input current can be increased.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2019/107419, filed on Sep. 24, 2019, which claims priority toChinese Patent Application No. 201811543560.6, filed on Dec. 17, 2018.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to the field of power electronictechnologies, and in particular, to a phase alignment circuit and methodof a receive end, and a receive end.

BACKGROUND

With intensification of energy shortages and environmental pollution inthe modern society, electric vehicles have attracted wide attention fromall walks of life as new energy vehicles. However, most of existingelectric vehicles are limited by battery capacities and have arelatively short driving distance. In addition, the electric vehicle hasa long battery charging time and corresponding charging stationresources are scarce. This has become a biggest bottleneck restrictingapplication and popularization of the electric vehicles.

Battery charging methods for electric vehicles usually include: contactcharging and wireless charging. During contact charging, electricity isconducted through metal contact between a plug and a socket. Duringwireless charging, a coupled electromagnetic field is used as a mediumto transfer electrical energy. Compared with contact charging, wirelesscharging has many advantages and becomes a mainstream manner forcharging electric vehicles in the future.

A wireless charging system has undergone a development process of anon-tuning method for adjusting output power by using a direct currentconversion circuit, passive tuning for adjusting output power by usingpassive components such as an inductor and a capacitor, and performingan impedance adjustment by using a controllable switching transistor.

The impedance adjustment is to control synchronization between a bridgearm voltage of a rectifier of a receive end and an input current of therectifier. Therefore, a phase of the input current of the rectifierneeds to be detected. However, because the input current of therectifier generally has a harmonic signal or an interference signal, thedetected input current needs to be filtered. Regardless of whether thefiltering is hardware filtering or software filtering, a phase existingafter the filtering lags behind the phase existing before the filtering.

SUMMARY

To resolve the foregoing technical problem existing in the prior art,the present invention provides a phase alignment circuit and method of areceive end, and a receive end, so that a phase lag caused due tofiltering can be compensated for, to keep accurate synchronizationbetween a bridge arm voltage of a rectifier and an input current of therectifier.

According to a first aspect, an embodiment of this application providesa phase alignment circuit of a receive end, including: a phasemeasurement circuit and a controller. A first input end of the phasemeasurement circuit is connected to an output end of a current detectioncircuit, and a second input end of the phase measurement circuit isconnected to an output end of a filter. The current detection circuitdetects an input current of a rectifier. The filter filters the inputcurrent to obtain an input current fundamental component. The phasemeasurement circuit obtains a difference between a phase of the inputcurrent and a phase of the input current fundamental component. Thecontroller uses, as an actual phase shift angle, a result obtained bysubtracting the phase difference from a preset phase shift angle, andcontrols a phase of a bridge arm voltage of the rectifier to lag behindthe phase of the input current fundamental component by the actual phaseshift angle.

The phase alignment circuit can compensate for a phase lag caused due tofiltering, to keep accurate synchronization between the bridge armvoltage of the rectifier and the input current of the rectifier. Whenthe phase of the bridge arm voltage is controlled by using the phase ofthe input current as a reference, a phase difference caused due to afiltering delay needs to be subtracted from the preset phase shift anglebetween the bridge arm voltage that needs to be theoretically controlledand the input current, to compensate for the phase difference caused dueto filtering. The controller outputs a drive signal for a controllableswitching transistor of the rectifier by using the actual phase shiftangle. Because a lagging phase caused due to filtering is compensatedfor, precision of synchronization between the bridge arm voltage and theinput current can be increased.

The phase measurement circuit may be digital or analog. For example,when the phase measurement circuit is a digital phase detector, thephase alignment circuit further includes: a first zero-crossing detectorand a second zero-crossing detector. An input end of the firstzero-crossing detector is connected to the output end of the filter, andan input end of the second zero-crossing detector is connected to theoutput end of the current detection circuit. An output end of the firstzero-crossing detector is connected to a first input end of the digitalphase detector, and an output end of the second zero-crossing detectoris connected to a second input end of the digital phase detector. Thefirst zero-crossing detector is configured to perform zero-crossingdetection on the input current fundamental component, to obtain a firstsquare wave. The second zero-crossing detector is configured to performzero-crossing detection on the input current, to obtain a second squarewave. The digital phase detector is configured to obtain the differencebetween the phase of the input current and the phase of the inputcurrent fundamental component based on the first square wave and thesecond square wave. The digital phase detector may directly obtain adifference between phases of the two square wave signals, that is,obtain a phase difference in a form of a digital signal, and directlysend the phase difference to the controller. The controller may directlyprocess the digital signal, thereby saving resources of the controller.

When the phase measurement circuit is an analog phase detector, thephase alignment circuit further includes: an analog to digitalconverter. A first input end of the analog phase detector is connectedto the output end of the current detection circuit, and a second inputend of the analog phase detector is connected to the output end of thefilter. The analog to digital converter is configured to perform analogto digital conversion on a phase difference that is output by the analogphase detector, to obtain a phase difference in a form of a digitalsignal. Because the analog phase detector can receive an analog signal,the analog phase detector can directly process a sine signal. Therefore,no zero-crossing detector needs to perform zero-crossing detection toobtain a square wave signal.

In an embodiment, the analog to digital converter and the controller areintegrated together. In other words, the controller may have its ownanalog to digital converter.

In an embodiment, the rectifier is a full-bridge rectifier, and thefull-bridge rectifier includes four controllable switching transistors.The bridge arm voltage is a voltage between a middle point of a leadingbridge arm of the full-bridge rectifier and a middle point of a laggingbridge arm of the full-bridge rectifier. The rectifier is a half-bridgerectifier, and the half-bridge rectifier includes two controllableswitching transistors. The bridge arm voltage is a voltage between amiddle point of a bridge arm of the half-bridge rectifier and theground.

In an embodiment, the preset phase shift angle is 0, or the preset phaseshift angle is a fixed preset value greater than 0.

According to a second aspect, an embodiment of this application providesa phase alignment method of a receive end, where the method is appliedto the foregoing phase alignment circuit, and includes: detecting aninput current of a rectifier; filtering the input current of therectifier to obtain an input current fundamental component; obtaining adifference between a phase of the input current and a phase of the inputcurrent fundamental component; and using, as an actual phase shiftangle, a result obtained by subtracting the phase difference from apreset phase shift angle, and controlling a phase of a bridge armvoltage of the rectifier to lag behind the phase of the input currentfundamental component by the actual phase shift angle.

Based on the method, a phase lag caused due to filtering can becompensated for, to keep accurate synchronization between the bridge armvoltage of the rectifier and the input current of the rectifier. Whenthe phase of the bridge arm voltage is controlled by using the phase ofthe input current as a reference, a phase difference caused due to afiltering delay needs to be subtracted from the preset phase shift anglebetween the bridge arm voltage that needs to be theoretically controlledand the input current, to compensate for the phase difference caused dueto filtering. A drive signal for a controllable switching transistor ofthe rectifier is output by using the actual phase shift angle. Because alagging phase caused due to filtering is compensated for, precision ofsynchronization between the bridge arm voltage and the input current canbe increased.

According to a third aspect, an embodiment of this application furtherprovides a receive end, including: a receiving coil, a rectifier, andthe foregoing phase alignment circuit. The receiving coil receiveselectromagnetic energy transmitted by a transmitting coil and outputs analternating current. The rectifier rectifies the alternating currentinto a direct current. The phase alignment circuit aligns a phase of abridge arm voltage of the rectifier based on a difference between aphase of an input current existing before filtering and a phase of aninput current existing after the filtering of the rectifier.

The receive end may be applied to a wireless charging system, and thewireless charging system may charge an electric vehicle. The receive endmay be located on the electric vehicle, and charge a power battery packon the electric vehicle.

The rectifier is a full-bridge rectifier or a half-bridge rectifier.When the rectifier is the full-bridge rectifier, four controllableswitching transistors may be included, or only two controllableswitching transistors may be included. When the rectifier is thehalf-bridge rectifier, two included switching transistors are bothcontrollable switching transistors.

Compared with the prior art, the present invention has at least thefollowing advantages:

The phase lag caused due to filtering can be compensated for, to keepaccurate synchronization between the bridge arm voltage of the rectifierand the input current of the rectifier. Specifically, a phase existingafter filtering lags behind an actual phase of the input current, andthe phase of the bridge arm voltage is also usually enabled to lagbehind the phase of the input current; or certainly, the phase of thebridge arm voltage may be the same as the phase of the input current.Therefore, when the phase of the bridge arm voltage is controlled byusing the phase of the input current as a reference, the phasedifference caused due to the filtering delay needs to be subtracted fromthe preset phase shift angle between the bridge arm voltage that needsto be theoretically controlled and the input current, to compensate forthe phase difference caused due to filtering. The controller outputs thedrive signal for the controllable switching transistor of the rectifierby using the actual phase shift angle. Because the lagging phase causeddue to filtering is compensated for, precision of synchronizationbetween the bridge arm voltage and the input current can be increased.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of thisapplication more clearly, the following briefly describes theaccompanying drawings required for describing the embodiments or theprior art. Apparently, the accompanying drawings in the followingdescription show some embodiments of this application, and a person ofordinary skill in the art may still derive other drawings from theseaccompanying drawings without creative efforts.

FIG. 1 is an equivalent circuit diagram of a wireless charging system;

FIG. 2 is a schematic diagram of a phase alignment circuit according toan embodiment of this application;

FIG. 3 is a schematic diagram of another phase alignment circuitaccording to an embodiment of this application;

FIG. 4 is a schematic diagram of still another phase alignment circuitaccording to an embodiment of this application;

FIG. 5 is a schematic diagram of yet another phase alignment circuitaccording to an embodiment of this application;

FIG. 6 is a phase alignment waveform graph according to an embodiment ofthis application;

FIG. 7 is a schematic diagram of a rectifier that is a full-bridgerectifier according to an embodiment of this application;

FIG. 8 is another schematic diagram of a rectifier that is a full-bridgerectifier according to an embodiment of this application;

FIG. 9 is a schematic diagram of a rectifier that is a half-bridgerectifier according to an embodiment of this application;

FIG. 10 is a flowchart of a phase alignment method according to anembodiment of this application; and

FIG. 11 is a schematic diagram of a wireless charging system accordingto an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

To enable a person skilled in the art to better understand technicalsolutions provided in the embodiments of this application, anapplication scenario of the embodiments of this application is firstdescribed below.

FIG. 1 is an equivalent circuit diagram of a wireless charging system.

The wireless charging system includes a transmit end and a receive end.The transmit end includes an inverter, a compensation circuit 100, and atransmitting coil Ct. The inverter includes four switching transistorsQ1 to Q4.

The receive end includes a receiving coil Cr, a compensation circuit200, and a rectifier. The rectifier includes four switching transistorsS1 to S4.

Electromagnetic energy is usually wirelessly transferred between thetransmit end and the receive end. In other words, the transmit endtransmits electromagnetic energy, and the receive end receives, throughwireless communication, the electromagnetic energy transmitted by thetransmit end.

During an impedance adjustment, the rectifier of the receive end needsto be controlled, to control synchronization between a bridge armvoltage of the rectifier and an input current i of the rectifier. Therectifier may be a full-bridge rectifier or a half-bridge rectifier.FIG. 1 shows the full-bridge rectifier. The full-bridge rectifierincludes four switching transistors. In this case, the bridge armvoltage of the rectifier is a voltage between middle points of twobridge arms of the rectifier, that is, U2 in the figure. When therectifier is the half-bridge rectifier, the bridge arm voltage is avoltage between a middle point of a bridge arm of the rectifier and theground.

Keeping synchronization between the bridge arm voltage of the rectifierand the input current of the rectifier means that cycles or frequenciesof the two are the same. In a process of keeping synchronization betweenthe cycle of the bridge arm voltage and the cycle of the input current,a fixed phase difference may be kept between the two. The fixed phasedifference may be 0, or may be a preset fixed value greater than 0.

If the cycles or frequencies of the two are the same, a phase of theinput current of the rectifier needs to be obtained, to obtain the cycleof the input current, so that the bridge arm voltage follows the cycleof the input current.

However, when the phase of the input current of the rectifier isdetected, because the input current of the rectifier generally has aharmonic signal or an interference signal, the detected input currentneeds to be filtered. Regardless of whether the filtering is hardwarefiltering or software filtering, a phase existing after the filteringlags behind the phase existing before the filtering.

Therefore, based on a phase alignment circuit and method and a systemthat are provided in the embodiments of this application, a phase lagcaused due to filtering can be compensated for, to keep accuratesynchronization between the bridge arm voltage of the rectifier and theinput current of the rectifier. In an embodiment, the phase existingafter the filtering lags behind an actual phase of the input current,and in a controller, a phase of the bridge arm voltage is also usuallyenabled to lag behind the phase of the input current; or certainly, aphase of the bridge arm voltage may be the same as the phase of theinput current. Therefore, when the phase of the bridge arm voltage iscontrolled by using the phase of the input current as a reference, aphase difference caused due to a filtering delay needs to be subtractedfrom a preset phase shift angle between the bridge arm voltage thatneeds to be theoretically controlled and the input current, tocompensate for the phase difference caused due to filtering.

To make a person skilled in the art understand the technical solutionsin the present invention better, the following clearly describes thetechnical solutions in the embodiments of the present invention withreference to the accompanying drawings in the embodiments of the presentinvention. Apparently, the described embodiments are merely some ratherthan all of the embodiments of the present invention. All otherembodiments obtained by a person of ordinary skill in the art based onthe embodiments of the present invention without creative efforts shallfall within the protection scope of the present invention.

Alignment Circuit Embodiment 1

FIG. 2 is a schematic diagram of a phase alignment circuit according toan embodiment of this application.

An example in which a rectifier is a full-bridge rectifier is used inthis embodiment for description. As shown in FIG. 2, the rectifierincludes controllable switching transistors S1 to S4. A bridge armvoltage of the rectifier is U2.

The phase alignment circuit for an impedance adjustment provided in thisembodiment includes a phase measurement circuit 300 and a controller400.

A first input end of the phase measurement circuit 300 is connected toan output end of a current detection circuit 500, and a second input endof the phase measurement circuit 300 is connected to an output end of afilter 600.

The current detection circuit 500 detects an input current of therectifier.

A specific implementation of the current detection circuit 500 is notlimited in this embodiment of this application, and for example, thecurrent detection circuit 500 may be a Hall effect sensor or a currenttransformer (CT).

The filter 600 filters the input current to obtain an input currentfundamental component.

A main role of the filter 600 is to filter out a high-order harmonic inthe input current and retain the input current fundamental component.

The filter 600 may use a relatively mature filter circuit.

The phase measurement circuit 300 obtains a difference between a phaseof the input current and a phase of the input current fundamentalcomponent.

The phase measurement circuit 300 may be implemented by using a phasedetector, or may be implemented by using a circuit built by a basiccircuit device, and is mainly configured to obtain a difference betweenphases of two input signals.

The controller 400 uses, as an actual phase shift angle, a resultobtained by subtracting the phase difference from a preset phase shiftangle, and controls a phase of the bridge arm voltage of the rectifierto lag behind the phase of the input current fundamental component bythe actual phase shift angle.

For ease of description, the preset phase shift angle is represented byδ and the phase difference is represented by β in the following.

The filter causes a delay to the phase of the input current. Therefore,when generating a drive signal for a controllable switching transistorof the rectifier, the controller needs to compensate for a phasedifference caused due to the delay. Keeping synchronization between thebridge arm voltage of the rectifier and the input current of therectifier means keeping synchronization with the input current existingbefore the filtering.

Before filtering, the input current of the rectifier is a sine signalincluding a harmonic. After filtering, the input current becomes a sinesignal. However, a phase of the sine signal existing after filteringlags behind, by the phase difference β, a phase of the sine signalexisting before filtering.

If the preset phase shift angle between the bridge arm voltage of therectifier and the input current of the rectifier is δ, a phase shiftangle of the bridge arm voltage to the input current fundamentalcomponent needs to be actually controlled to be δ−β.

The preset phase shift angle δ is a preset value, and may be 0 or may bea fixed preset value.

Based on the alignment circuit provided in this embodiment, an inputcurrent existing before filtering and an input current existing afterthe filtering the rectifier are obtained, to obtain a difference betweena phase of the input current existing before the filtering and a phaseof the input current existing after the filtering. Because the phasedifference is caused due to filtering, the phase difference needs to besubsequently controlled to be compensated for. In this embodiment, thecontroller uses, as the actual phase shift angle, the result obtained bysubtracting the phase difference from the preset phase shift angle, andcontrols the phase of the bridge arm voltage of the rectifier to lagbehind the phase of the input current fundamental component by theactual phase shift angle. The controller outputs the drive signal forthe controllable switching transistor of the rectifier by using theactual phase shift angle. Because a lagging phase caused due tofiltering is compensated for, precision of synchronization between thebridge arm voltage and the input current can be increased.

Alignment Circuit Embodiment 2

FIG. 3 is a schematic diagram of another phase alignment circuitaccording to an embodiment of this application.

In the phase alignment circuit provided in this embodiment, the phasemeasurement circuit may be a digital phase detector 301.

The phase alignment circuit further includes: a first zero-crossingdetector 700 and a second zero-crossing detector 800.

An input end of the first zero-crossing detector 700 is connected to theoutput end of the filter 600, and an input end of the secondzero-crossing detector 800 is connected to the output end of the currentdetection circuit 500. An output end of the first zero-crossing detector700 is connected to a first input end of the digital phase detector 301,and an output end of the second zero-crossing detector 800 is connectedto a second input end of the digital phase detector 301.

The first zero-crossing detector 700 is configured to performzero-crossing detection on the input current fundamental component, toobtain a first square wave.

The second zero-crossing detector 800 is configured to performzero-crossing detection on the input current, to obtain a second squarewave.

The current detection circuit 500 outputs a sine signal having aharmonic, and the filter 600 outputs a sine signal. Because only adigital signal can be processed when the phase measurement circuit usesthe digital phase detector 301, an analog signal corresponding to a sinesignal needs to be converted into a digital signal. Therefore, in thisembodiment of this application, a sine signal is converted into a squarewave signal with a same phase and cycle by using a zero-crossingdetector. Because the square wave signal belongs to a digital signal,the square wave signal can be directly processed by the digital phasedetector 301.

The digital phase detector 301 is configured to obtain a differencebetween a phase of the input current and a phase of the input currentfundamental component based on the first square wave and the secondsquare wave.

The digital phase detector 301 may obtain a difference between phases ofthe two square wave signals, and the phase difference is a differencebetween phases of input currents that is caused by the filter.

In an embodiment, a difference between a phase of an input currentexisting before filtering and a phase of an input current existing afterthe filtering is obtained by using the digital phase detector 301.Because a signal received by the digital phase detector 301 needs to bea digital signal and an analog signal cannot be processed, the firstzero-crossing detector 700 and the second zero-crossing detector 800need to separately perform zero-crossing detection to convert a sinesignal into a square wave signal. The digital phase detector 301 maydirectly obtain the difference between the phases of the two square wavesignals, that is, obtain a phase difference in a form of a digitalsignal, and directly send the phase difference to the controller 400.The controller 400 may directly process the digital signal, therebysaving resources of the controller 400.

Remaining content of this embodiment is the same as that in Embodiment 1of the phase alignment circuit. Details are not described herein.

Embodiment 2 of the alignment circuit is described by using an examplein which the phase measurement circuit is the digital phase detector,and an implementation in which the phase measurement circuit is ananalog phase detector is described below.

Phase Alignment Circuit Embodiment 3

FIG. 4 is a schematic diagram of still another phase alignment circuitaccording to an embodiment of this application.

In the phase alignment circuit provided in this embodiment, the phasemeasurement circuit is an analog phase detector 302.

The phase alignment circuit further includes an analog to digitalconverter 401.

A first input end of the analog phase detector 302 is connected to theoutput end of the current detection circuit 500, and a second input endof the analog phase detector 302 is connected to the output end of thefilter 600.

The analog to digital converter 401 is configured to: perform analog todigital conversion on a phase difference that is output by the analogphase detector 302, convert the phase difference into a phase differencein a form of a digital signal, and send the phase difference in the formof the digital signal to the controller 400.

The controller 400 processes the phase difference in the form of thedigital signal.

According to the phase alignment circuit provided in this embodiment, adifference between a phase of an input current existing before filteringand a phase of an input current existing after the filtering is obtainedby using the analog phase detector 302. Because the analog phasedetector 302 can receive an analog signal, the analog phase detector 302can directly process a sine signal. Therefore, no zero-crossing detectorneeds to perform zero-crossing detection to obtain a square wave signal.Because the analog phase detector 302 outputs a phase difference in aform of an analog signal, the analog to digital converter needs toconvert the phase difference into a phase difference in a form of adigital signal, and then the controller 400 can directly process thephase difference.

It may be understood that the analog to digital converter 401 and thecontroller 400 may be integrated together, that is, the analog todigital converter 401 is integrated in the controller 400. For details,refer to the circuit diagram shown in FIG. 5.

To enable a person skilled in the art to more intuitively understand thetechnical solutions provided in the embodiments of this application,detailed descriptions are provided below with reference to a waveformgraph corresponding to FIG. 3.

FIG. 6 is a phase alignment waveform graph according to an embodiment ofthis application.

It can be seen from FIG. 6 that a waveform of an input current i of arectifier corresponds to a waveform existing before filtering and awaveform existing after filtering that are both sine waves. A solid lineindicates an input current existing before filtering, and a dashed lineindicates an input current existing after the filtering.

A square wave that is output by a first zero-crossing detectorcorresponds to a square wave signal obtained by performing zero-crossingdetection on a sine signal existing before i is filtered, and a squarewave that is output by a second zero-crossing detector corresponds to asquare wave signal obtained by performing zero-crossing detection on asine signal after i is filtered.

It can be seen from the figure that a phase existing after i is filteredlags, by a phase difference β, behind a phase existing before i isfiltered, in other words, a difference between a phase of a signal thatis output by the first zero-crossing detector and a phase of a signalthat is output by the second zero-crossing detector is β.

If an expected phase shift angle between a bridge arm voltage and theinput current is a preset phase shift angle δ, if by using a phase of aninput current fundamental component existing after filtering as areference, a phase of the bridge arm voltage is controlled to lag, by δ,behind the phase of the input current fundamental component existingafter filtering, a phase difference by which the phase of the bridge armvoltage lags behind a phase of an actual input current fundamentalcomponent is δ+β. Therefore, the phase shift angle δ between the phaseof the bridge arm voltage and the phase of the input current fundamentalcomponent needs to be obtained by using the phase of the input currentexisting before the filtering as a reference. Therefore, the phase ofthe input current fundamental component existing after filtering needsto be compensated for, and a result obtained by subtracting the phasedifference β caused due to filtering from the preset phase shift angle δneeds to be used as a phase shift angle that is used to actually controla drive signal. In this way, a phase of an actually obtained bridge armvoltage lags behind the phase of the actual input current fundamentalcomponent by δ.

The foregoing embodiments are all described by using an example in whichthe rectifier is the full-bridge rectifier, and the four switchingtransistors of the full-bridge rectifier are all controllable switchingtransistors. Other implementations of the rectifier are described belowwith reference to the accompanying drawings. For example, when therectifier is the full-bridge rectifier, two controllable switchingtransistors and two diodes may be included. Detailed descriptions areprovided below with reference to the accompanying drawings.

FIG. 7 is a schematic diagram of a rectifier including two controllableswitching transistors according to an embodiment of this application.

As shown in FIG. 7, either of two bridge arms of the rectifier includesone controllable switching transistor and one diode. For example, aleading bridge arm includes a first diode D1 and a first controllableswitching transistor S3, and a lagging bridge arm includes a seconddiode D2 and a second controllable switching transistor S4.

Locations of the two diodes and locations of the two controllableswitching transistors in FIG. 7 are interchangeable.

FIG. 8 is another schematic diagram of a rectifier including twocontrollable switching transistors according to an embodiment of thisapplication.

The rectifier shown in FIG. 8 also includes two diodes and twocontrollable switching transistors.

One bridge arm includes two diodes D1 and D3, and another bridge armincludes two controllable switching transistors S2 and S4.

It may be understood that locations of switching transistors on the twobridge arms are interchangeable.

The full-bridge rectifier is described above, and a half-bridgerectifier is described below. A bridge arm voltage of the full-bridgerectifier is a voltage between middle points of two bridge arms. Abridge arm voltage of the half-bridge rectifier is a voltage between amiddle point of a bridge arm and the ground.

FIG. 9 is a schematic diagram of a rectifier that is a half-bridgerectifier according to an embodiment of this application.

Two switching transistors of the half-bridge rectifier are bothcontrollable switching transistors: S1 and S3 shown in FIG. 9.

A specific implementation of the rectifier is not limited in thisembodiment of this application. A person skilled in the art may performselection depending on an actual product requirement.

Method Embodiment

Based on the phase alignment circuit provided in the foregoingembodiment, this embodiment of this application further provides a phasealignment method. Detailed descriptions are provided below withreference to the accompanying drawing.

FIG. 10 is a flowchart of a phase alignment method of a receive endaccording to an embodiment of this application.

The phase alignment method provided in this embodiment is applied to thephase alignment circuit provided in any one of the foregoingembodiments, and includes the following operations.

S101: Detect an input current of a rectifier.

In an embodiment, detection may be performed by using a current sensor.A type of the current sensor is not specifically limited in thisembodiment of this application, and for example, the current sensor maybe a Hall effect sensor or may be a current transformer.

S102: Filter the input current of the rectifier to obtain an inputcurrent fundamental component.

Because the directly detected input current has a harmonic component,the harmonic component needs to be filtered out to obtain the inputcurrent fundamental component, and a subsequently to-be-processed objectis the input current fundamental component.

S103: Obtain a difference between a phase of the input current and aphase of the input current fundamental component.

A phase delay is caused due to filtering. Therefore, to compensate, in asubsequent operation, for the phase difference caused by the delay, thephase difference needs to be obtained.

S104: Use, as an actual phase shift angle, a result obtained bysubtracting the phase difference from a preset phase shift angle, andcontrol a phase of a bridge arm voltage of the rectifier to lag behindthe phase of the input current fundamental component by the actual phaseshift angle.

An input current existing before filtering and an input current existingafter the filtering of the rectifier are obtained, to obtain adifference between a phase of the input current existing before thefiltering and a phase of the input current existing after the filtering.Because the phase difference is caused due to filtering, the phasedifference needs to be subsequently controlled to be compensated for. Inthis embodiment, the controller uses, as the actual phase shift angle,the result obtained by subtracting the phase difference from the presetphase shift angle, and controls the phase of the bridge arm voltage ofthe rectifier to lag behind the phase of the input current fundamentalcomponent by the actual phase shift angle. The controller outputs adrive signal for a controllable switching transistor of the rectifier byusing the actual phase shift angle. Because a lagging phase caused dueto filtering is compensated for, precision of synchronization betweenthe bridge arm voltage and the input current can be increased.

Receive-End Embodiment

Based on the phase alignment circuit and method provided in theforegoing embodiments, this embodiment of this application furtherprovides a receive end of a wireless charging system. Detaileddescriptions are provided below with reference to the accompanyingdrawing.

FIG. 11 is a schematic diagram of a wireless charging system accordingto an embodiment of this application.

It may be understood that the wireless charging system may be applied tovarious fields in which wireless charging is required, for example, theelectric vehicle field. A receive end may be located on an electricvehicle and be used as a vehicle-mounted terminal. However, a transmitend of the wireless charging system may be located on the ground, andthe transmit end wirelessly charges the electrical vehicle.Specifically, a transmitting coil of the transmit end transmits analternating magnetic field, and a receiving coil of the receive endreceives the alternating magnetic field, so as to exchangeelectromagnetic energy.

As shown in FIG. 11, the wireless charging system provided in thisembodiment includes the receive end and the transmit end, and thereceive end includes an inverter, a first compensation circuit 100, anda transmitting coil Ct. The inverter includes four controllableswitching transistors Q1 to Q4.

The receive end includes: a receiving coil Cr, a second compensationcircuit 200, a rectifier, and the phase alignment circuit 1000 describedin any one of the foregoing embodiments. The rectifier is described byusing an example of a full-bridge rectifier including four controllableswitching transistors S1 to S4.

The receiving coil Cr receives electromagnetic energy transmitted by thetransmitting coil Ct and outputs an alternating current.

The rectifier rectifies the alternating current into a direct current tosupply power to a powered device. For example, in the electric vehiclefield, load of the rectifier may be a power battery on an electricvehicle.

In an embodiment, the phase alignment circuit 1000 may align a phase ofa bridge arm voltage of the rectifier based on a difference between aphase of an input current existing before filtering and a phase of aninput current existing after the filtering of the rectifier.

In addition to the full-bridge rectifier shown in FIG. 11, the rectifiermay alternatively be a half-bridge rectifier.

The receive end provided in this embodiment obtains the input currentexisting before the filtering and the input current existing after thefiltering of the rectifier, to obtain the difference between the phaseof the input current existing before the filtering and the phase of theinput current existing after the filtering. Because the phase differenceis caused due to filtering, the phase difference needs to besubsequently controlled to be compensated for. In this embodiment, aresult obtained by subtracting the phase difference from a preset phaseshift angle is used as an actual phase shift angle, and the phase of thebridge arm voltage of the rectifier is controlled to lag behind a phaseof an input current fundamental component by the actual phase shiftangle. The controller outputs a drive signal for a controllableswitching transistor of the rectifier by using the actual phase shiftangle. Because a lagging phase caused due to filtering is compensatedfor, precision of synchronization between the bridge arm voltage of therectifier and the input current can be increased.

An embodiment of this application further provides a wireless chargingsystem including the receive end described in the foregoing embodiment.The wireless charging system may be applied to the electric vehiclefield.

It should be understood that, in this application, “at least one (item)”means one or more, and “a plurality of” means two or more than two.“And/or” is used to describe an association relationship betweenassociated objects and represents that three relationships may exist.For example, “A and/or B” may represent: Only A exists, only B exists,and both A and B exist. Either of A and B may be singular or plural. Thecharacter “/” generally indicates an “or” relationship between theassociated objects. “At least one (item) of the following” or a similarexpression thereof refers to any combination of the items, including anycombination of one or more (items). For example, at least one (item) ofa, b, or c may indicate: a, b, c, “a and b”, “a and c”, “b and c”, or“a, b, and c”. Each of a, b, and c may be singular or plural.

The foregoing are merely embodiments of the present invention, and arenot intended to limit the present invention in any form. Although thepresent invention has been disclosed as above with preferredembodiments, it is not intended to limit the present invention. By usingthe method and the technical content disclosed above, any person ofordinary skill in the art can make a plurality of possible changes andmodifications to the technical solutions of the present invention, oramend the technical solutions thereof to be embodiments with equaleffects through equivalent variations without departing from theprotection scope of the technical solutions of the present invention.Therefore, without departing from the content of the technical solutionsof the present invention, any simple modification, equivalent change,and modification made to the foregoing embodiments according to thetechnical essence of the present invention still fall within theprotection scope of the technical solutions of the present invention.

What is claimed is:
 1. A phase alignment circuit of a receive end,comprising: a phase measurement circuit having a first input end and asecond input end, the first input end being connected to an output endof a current detection circuit, the second input end being connected toan output end of a filter, wherein the current detection circuit is todetect an input current of a rectifier, and the filter is to filter theinput current to obtain an input current fundamental component, andwherein the phase measurement circuit is further to obtain a phasedifference between a phase of the input current and a phase of the inputcurrent fundamental component, wherein the phase measurement circuit isa digital phase detector; a controller configured to: determine anactual phase shift angle by subtracting the phase difference from apreset phase shift angle, and control a phase of a bridge arm voltage ofthe rectifier to lag behind the phase of the input current fundamentalcomponent by the actual phase shift angle; a first zero-crossingdetector having an input end connected to the output end of the filterand an output end connected to a first input end of the digital phasedetector, wherein the first zero-crossing detector is to performzero-crossing detection on the input current fundamental component toobtain a first square wave; and a second zero-crossing detector havingan input end connected to the output end of the current detectioncircuit and an output end connected to a second input end of the digitalphase detector, wherein the second zero-crossing detector is to performzero-crossing detection on the input current to obtain a second squarewave, wherein the digital phase detector is configured to obtain thephase difference between the phase of the input current and the phase ofthe input current fundamental component based on the first square waveand the second square wave.
 2. The phase alignment circuit according toclaim 1, wherein the rectifier is a full-bridge rectifier comprisingfour controllable switching transistors, and wherein the bridge armvoltage is a voltage between a middle point of a leading bridge arm ofthe full-bridge rectifier and a middle point of a lagging bridge arm ofthe full-bridge rectifier.
 3. The phase alignment circuit according toclaim 1, wherein the rectifier is a half-bridge rectifier comprising twocontrollable switching transistors, and wherein the bridge arm voltageis a voltage between a middle point of a bridge arm of the half-bridgerectifier and the ground.
 4. The phase alignment circuit according toclaim 1, wherein the preset phase shift angle is 0, or the preset phaseshift angle is a fixed preset value greater than
 0. 5. A receive end,comprising: a receiving coil and the phase alignment circuit accordingto claim 1, wherein the receiving coil is configured to receiveelectromagnetic energy transmitted by a transmitting coil and output analternating current; and the rectifier is configured to rectify thealternating current into a direct current.
 6. The receive end accordingto claim 5, wherein the rectifier is a full-bridge rectifier or ahalf-bridge rectifier.
 7. A phase alignment method of a receive end,comprising: detecting an input current of a rectifier; filtering theinput current of the rectifier to obtain an input current fundamentalcomponent; obtaining a phase difference between a phase of the inputcurrent and a phase of the input current fundamental component;determining an actual phase shift angle by subtracting the phasedifference from a preset phase shift angle; controlling a phase of abridge arm voltage of the rectifier to lag behind the phase of the inputcurrent fundamental component by the actual phase shift angle;performing zero-crossing detection on the input current fundamentalcomponent to obtain a first square wave; performing zero-crossingdetection on the input current to obtain a second square wave; andobtaining the phase difference between the phase of the input currentand the phase of the input current fundamental component based on thefirst square wave and the second square wave.
 8. The method according toclaim 7, wherein the rectifier is a full-bridge rectifier comprisingfour controllable switching transistors, and wherein the bridge armvoltage is a voltage between a middle point of a leading bridge arm ofthe full-bridge rectifier and a middle point of a lagging bridge arm ofthe full-bridge rectifier.
 9. The method according to claim 7, whereinthe rectifier is a half-bridge rectifier comprising two controllableswitching transistors, and wherein the bridge arm voltage is a voltagebetween a middle point of a bridge arm of the half-bridge rectifier anda ground.
 10. The method according to claim 7, wherein the preset phaseshift angle is 0, or the preset phase shift angle is a fixed presetvalue greater than 0.